Method of degreasing



y 2, 4 J. AVA E 2,123,439

METXiOD OF DEGREASING Original Filed May 5, 1933 31 \30 INVENTOR.

osepa SAVAGE VATYTORNEX .as trichlorethylene.

Patented July 12,

METHOD OF. DEGREASING Joseph Savage, Weston Point, Bnncorn, England,

assignor to Imperial Chemical Industries Limited, a corporation of GreatBritain Original application May 5, 1933, Serial No.

Divided and this application October 7, 1935, Serial No. 43,888. InGreat Britain May 6, 1932 1 Claim.

This invention relates to an improved method for degreasing by means ofvolatile solvents such This application is a division of my copendingapplication S. N. 669,610, filed May 5, 1933 now Patent No. 2,020,335issued Nov. 12, 1935.

A large number of methods and types of apparatus have been proposed forthe removal of grease and fat from various types of material, in whichcooling surfaces are employed for the cooling and condensation of thevapours of the volatile solvent,'the condensate being subsequentlyreturned to the apparatus. In some cases the cooling surfaces are usedfor cooling a body of liquid solvent or a chamber through whichmaterials to be degreased are passed before or during treatment.

Experience has shown that these cooling suri faces have a tendency tocondense water from the atmosphere in addition to cooling and condensingthe solvent. This condensed water then becomes associated with thesolvent and thus comes into contact with the metal parts of theapparatus and with the material being treated. This increases thetendency of the metals to corrode and is .particularly objectionable inthe degreasing of metal goods such as iron or steel.

According to the invention .I warm, to apredetermined extent, thecooling waterwhich is used and thereby maintain the cooling andcondensing surfaces at a temperature above the dew point of theatmosphere in which the operation is carried out, but substantiallybelow the condensing temperature of the solvent. As a further feature ofthe invention, the solvent vapours are first brought into contact withthe said cooling surfaces and then uncondensed vapours are brought intocontact with still cooler surfaces. The condensate from these lastsurfaces, which may be a mixture of solvent and water, is collectedseparately from that of the solvent vapour obtained from the firstcooling surfaces. Complete condensation is thus effected while at thesame time the main bulk of condensate remains uncontaminated by water.In the degreasing of metal goods by means volatile solvents, the processmay be carried out in the vapour phase or in the liquid phase, that isthe goods may be exposed to the vapour of a volatile solvent or may bewashed by a hot or cold liquid solvent. Combinations of these variousmethods of working may also be made. The present invention is of courseonly applicable to processes involving vapour phase degreasing ortreatment of the goods with heated liquid solvent. In most forms ofapparatus for carrying out these processes the cooling surfaces consistof pipes through which a supply of cold water ows. In such cases Imaintain the desired temperature of the cooling surface by slightlywarming the inlet water before admitting to the cooling pipes. Thismaybe done in many ways, for example, by passing the water through a smallelectrical heater or gas heater, either of which may be convenientlycontrolled by a thermostatic device. This method is applicable whenvapour phase degreasing is used alone or when vapour-phase degreasingfollows a treatment with cold liqu'id solvent.

In an alternative method, in processes and apparatus using a degreasingbath of solvent liquor at a raised temperature and with cooling coilsarranged above the surface, I pass the cooling water through coilsarranged in such a heated bath prior to its passage through said'cooling coils. In this case the number of coils immersed in the liquidand the velocity of the cooling water are adjusted so that the desiredtemperature ofthe cooling surfaces is obtained. This method may also beapplied when the process is a combination of vapour phase and liquidphase degreasing using the liquid at an elevated temperature.

An apparatus adapted for. carrying out the process, referred to in thepreceding paragraph, is illustrated in the accompanying drawing, inwhich Figure 1 shows an elevation and Figure 2 a plan of the apparatus.Referring to Figure 1, the apparatus comprises an outer casing l insidewhich are located the degreasing chambers 2 and 3 adapted to hold a bodyof liquid, and separated by the wall 4. Chamber 2 is used for degreasingin the liquid phase and 3 for degreasing in the vapour phase. Bothchambers are open to the vapour space I2 in the upper portion of theeasing I. The wall 4 is preferably constructed in the form of a doublewall so as to possess an insulating value retarding the transference ofheat between the chambers 2 and 3. This enables the temperature of thechamber to be more easily controlled if it is desired to work below theboiling point of the solvent used.

Heating means are provided for each chamber: in the present case. thegas burners 5 and B are used for this purpose although suitably arrangedsteam coils or electrical heating devices may be used instead. Wastegases from the burners pass to the outlets I, I by way of the space 8left between the container 1 and the degreasing chambers 2 and 3. Thisspace, in addition to providing a path for the waste gases, also acts asan insulating jacket for the degreasing chambers and thus obviatesexcessive loss of heat by radiation.

to supply the vapour for the vapour phase degreasing. In. chamber 2 thethermostat may, if

desired, be used to control the temperature at some selected point belowthe boiling-point oi the solvent.

Cleaning doors in anddrain cocks H are fitted to the base of eachdegreasing chamber. In the I lower portion of each of the degreasingchambers perforated plates I! are fitted. These plates serve to carrythe goods being treated and must be so arranged as to permit the totalimmersion of the goods in the solvent liquid or vapour, and also in thecase of thechamber 3, to prevent contact of the goods with liquidsolventin the base of the chamber. 1

A set of coils I4 is arranged in the upper portion of the chamber 2.

obstruct the passage into and out of the chamber of goods being treated.A suitable connection i5 to the main2l, and provided with a valve 23 isiarranged for the supply of water to the coils and an outlet pipe llconnecting through the pipes and 25 to the condensing coils I9, isprovided. I also find that it is advantageous to fit a shield ll for theprotection of the coils ll against damage that might be caused byintroducing or withdrawing the goods.

Towards itsupper end the dividing wall 4 is provided with a smalloverflow outlet i8 leading from the chamber 2 to chamber 3 to enableexcess liquid in 2 to pass into 3 at a relatively slow rate. Thisoverflow is placed slightly higher than the cells it but at such adistance from the top of the wall 4 as to avoid a flow of liquid overthe top or the wall into chamber 3 when goods are introduced into thenormal volume of liquid in chamher 2. I

' In the upper portion of the casing I at any convenient height abovethe wall 4, condensing coils I! carried by the supports 20 are arrangedround the walls. The supply of water to these coils is from the coils Has previously stated and also.

from the main 2| through the pipe 22, fitted with a valve 24. and pipes25 and 28. At any convenient point after the junction of the pipes l6and 22 a pocket 21 carrying a thermometer is provided for the observanceof the temperature of the water entering the condensing coils. Theoutlet 28 for the water from the condensing coils leads to waste. Belowthe condensing coils, around the walls of the casing and adapted tocollect the condensate flowing from the coils and the walls of thecasing, is arranged a gutter or channel 29. Condensed solvent collectedby the gutter is delivered to the two-way cocl: 30 whence it flows byway of pipe ll back to the chamber 2 or by way of 32 to a receptacle notshown, for clean condensed solvent.

A suitable cover (not shown) may be provided for the apparatus toprevent the loss of solvent The coils are placed. I close to the wallsof the chamber in order not to mences to flow through the overflow ll.Solvent is also introduced-into the chamber 3, but in this case thevolume must be. adjusted sothat it's j surface is below the perforatedplate It even when it is in a state of ebullition. It will be obviousthat this is a necessary precaution if the efllcient degreasing of goodsresting on the plate I: is to be obtained, since after the apparatus hasbeen in use for'some' time the solvent becomes charged with dissolvedoils and if allowed to contact with the goods will leave a deposit orfilm of oil thereon which may not be removed while the goods are beingraised through the vapour prior to removal from the apparatus.

After charging the apparatus with solvent the temperature of the chamber2 is raised to the desired figure by means of the gas burner 5 and thesolvent in 3 is heated to boiling to provide for the vapour phasedegreasing. At the same time the condensing coils I! are put intooperation. The temperature of these coils is adjusted as required by theinvention by suitably. proportioning the feed of water through the coilsH to the feed coming directly from the main, the valves 23 and 24 beingprovided for this purpose. It would of course be possible to maintainthe water at the .required temperature by passing the whole supalsodesirable in order that any solid impurities such as swarf or dust,which may be adhering to the goods, may be removed by the mechanicalchamber '8 for removal of the. residual fllm of oily matter which iseffected by the' condensation thereon of the solvent. It will,'ofcourse, be obvious that when working in this manner the liquidphasedegreasing must be carried out at a temperature sufliciently belowthat at which the solvent boils, in order that the goods may condense anappreciable amount of solvent when'exposed to the vapour.

" Reference has previously been made to the desired temperature in theliquid phase degreasing chamber2. When working with trichlorethylenewashing action of the liquid. After this exposure 1 of the liquid, thegoodsare transferred to the I have found this to be about 20-30 0. belowin a solvent vapor bath and limiting the upward,

extent of said solvent vapor bath by condensing the residual vapours bybringing them first into contact with cooling surfaces maintained at atemperature above the dew point of the atmos- .phere in which theoperation is carried out, but

substantially below the condensing temperature of the solvent, and theninto contact with still cooler surfaces, the condensate from these lastsurfaces, which may be a mixture of solvent and water, being collectedseparately from that of the solvent vapours obtained from the firstcooling surfaces.

JOSEPH SAVAGE.

